Structure and morphology optimization of poly(3-hexylthiophene) thin films onto silanized silicon oxide

The influence of the preparation conditions, including substrate functionalization with common silanizers, onto structure/morphology of the overlying poly(3-hexylthiophene) thin films has been investigated by using both grazing incidence X-ray diffraction and atomic force microscopy. The factors determining the formation of spin-coated films suitable for applications in field effect transistors, i.e. concentration, spin-speed, and thermal treatment are addressed. We have established, by a tuning of the preparation and post-deposition treatments, the optimal conditions to get films with the required structural/morphologic features. Moreover we have shown that the macromolecules orient and organize at the interface zone (?10 nm from the interface) better than in the upper layers, i.e. far away from the interface.     

Fine tuning of a triply resonant OPO for generating frequency degenerate CV entangled beams at low pump powers

A method of achieving triple resonance in a frequency-degenerate but polarization-non-degenerate optical parametric oscillator (OPO) with external mirrors is illustrated. The OPO is brought to the triple-resonance condition by tuning the non-linear crystal temperature and tilting the cavity axis. The interplay among temperature and tilting mismatch and gain is analyzed together with the allowed ranges of variation of these parameters. The method has been successfully applied to an OPO based on a periodically poled KTP crystal. Calibration of the system is reported together with parametric gain and squeezing measurements below threshold as a test of reliability and efficiency. PACS 42.50.-p; 42.65.-k     

Trapped Ions Interacting with Laser Fields: a Perturbative Analysis without the Rotating Wave Approximation

The Hamiltonian describing a single ion placed in a potential trap in interaction with a laser beam is studied by means of a suitable perturbative approach. It is shown, in particular, that the rotating wave approximation does not provide the correct expression, already at the first perturbative order, of the evolution operator of the system.     

A uniqueness result for monotone elliptic problems

We give here a short proof of the uniqueness of entropy solutions for nonlinear monotone elliptic problems with L¹-data. To cite this article: M.M. Porzio, C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

On the multifractal analysis of Bernoulli convolutions. II. Dimensions

We show how the formalism developed in a previous paper allows us to exhibit the multifractal nature of the infinitely convolved Bernoulli measures for the golden mean. In this second part we show how the Hausdorff dimension of the set where the measure has a power law singularity of strength is related to the large-deviation function given in Part I.     

On the multifractal analysis of Bernoulli convolutions. I. Large-deviation results

We show how the formalism developed in a previous paper allows us to exhibit the multifractal nature of the infinitely convolved Bernoulli measures , for the golden mean. In this first part we establish some large-deviation results for random products of matrices, using perturbation theory of quasicompact operators.     

The dimension spectrum of some dynamical systems

We analyze the dimension spectrum previously introduced and measured experimentally by Jensen, Kadanoff, and Libchaber. Using large-deviation theory, we prove, for some invariant measures of expanding Markov maps, that the Hausdorff dimensionf() of the set on which the measure has a singularity is a well-defined, concave, and regular function. In particular, we show that this is the case for the accumulation of period doubling and critical mappings of the circle with golden rotation number. We also show in these particular cases that the functionf is universal.     

Non‐Resonant z‐Scan Characterization of the Third‐Order Nonlinear Optical Properties of Conjugated Poly(thiophene azines)

The nonlinear optical properties of a functionalized poly(thiophene azine), namely, poly(3,4‐didodecylthiophene azine), PAZ, at the optical telecommunication wavelength of 1550 nm are investigated by means of the closed‐aperture z‐scan technique in both thin films and solutions. Values of χ⁽³⁾=(2.4±0.4)×10^?13 esu, n₂=(4.0±0.7)×10^?15 cm² W^?1, and γ=(4.5±0.7)×10^?34 esu are estimated for the third‐order (Kerr) susceptibility, the intensity‐dependent refractive index, and the molecular second hyperpolarizability of solution samples, respectively. A very small dependence on the polymer chain length is found. Markedly higher values of (4.4±1.1)×10^?11 esu, (6.6±1.0)×10^?13 cm² W^?1, and (5.0±0.8)×10^?33 esu are measured for the corresponding quantities in thick (up to 20 μm) polymer films cast on quartz plates. The enhancement of the NLO responses on going from solution to solid samples is attributed to a partially ordered structure and to the presence of interchain interactions leading to greater π‐electron delocalization in the cast polymer films. The results are compared with those previously obtained by using third‐harmonic generation (THG), taking into account that those data were measured under conditions of three‐photon resonance, whereas our z‐scan measurements are fully off‐resonance.     

Phase Diagrams of Perhydrotriphenylene and Aromatic Compounds II. Terthiophene and related thiophene oligomers

Terthiophene included in a perhydrotriphenylene (PHTP) adduct exhibits an UV spectrum different from that observed in the bulk or in solution. The X-ray diffraction pattern also differs significantly from that of pure PHTP. The UV spectrum is interpreted as due to an isolated molecule in a vacuum-like space, in agreement with a model developed from X-ray diffraction data. Knowledge of the phase diagram was essential for an interpretation of the optical properties and of some kinetic aspects of the formation of the inclusion compound phase. In this work, the phase diagrams of terthiophene (T3) are presented, and DSC evidence of the inclusion of quater- (T4), penta- (T5)and α,ω-dihexylquaterthiophene (DH4T) is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.